The present invention relates to tensioning devices for drive systems and specifically to drive systems utilizing flexible drive elements such as belts and chains.
The present invention is adapted for use with a conventional drive system in which a driven member and drive member, such as pulleys or sprockets, are connected by a flexible drive element such as a belt or chain. Typically, the driven member is coupled to a motor directly or indirectly through a reduction gear system and the drive member is attached to an input drive shaft protruding from a piece of machinery. In such an arrangement, it is well know that the proper functioning of the drive system and the operating life of the drive system and flexible drive element can be significantly enhanced by maintaining the two flexible drive element runs between the drive and driven members in tension such that significant slack does not occur in either run. One method of providing such tension is to resiliently bias the drive and driven members away from one another. However, a more common and typically more convenient arrangement is to provide a tensioning device that biases one or both flexible drive element runs inward towards the other run at a point intermediate of the drive and driven members. A number of examples of this latter type of tensioning device are disclosed in the prior art. However, in the great majority of prior tensioning devices, the tensioning device is adapted to operate in a particular drive system and can not be used as a universal tensioning device capable of application in drive systems containing a wide range of combinations of flexible drive elements and drive and driven members.
One result of the fact that prior tensioning devices have been adapted for specific applications is that in many cases, prior tensioning devices have been mounted or secured to a support that is fixed with respect to the drive and driven members. Through use of such a support arrangement, the position of the tensioning device between the drive and driven members can be controlled, to maintain the tensioning at the optimum position.
A further feature of many prior art tensioning devices is that in such devices, the surfaces contacting the two runs of the drive element and urging them inward have either been fixed in position with respect to one another, or resiliently biased towards one another by springs or similar means. A disadvantage of the resilient biasing technique is that it adds complexity to the tensioning device, and the resiliently biased elements are subject to increased wear over time. Tensioning devices having fixed distances between their contact surfaces cannot be adjusted as the flexible drive element experiences wear. Thus, the tensioning force provided by the device decreases over time. A further disadvantage of a fixed distance between contact surfaces is that the tensioning device cannot be used with different sized drive and driven members or flexible drive elements.
Another disadvantage of prior art devices is that the tensioning device completely encircles the flexible drive element. For example, the flexible drive element is encircled by tensioning members such as rollers or sprockets on the top and bottom, and on each side by connecting members, such as straps, which couple the tensioning members a fixed distance apart. Inasmuch as the tensioning device completely encircles the upper and lower runs of the flexible drive element, the tensioning device can not be removed from the flexible drive element without disassembling the tensioning device, such as by removing a strap from one side of the tensioning device, or by removing the flexible drive element from at least one of the drive or driven members and sliding the tensioning device off that xe2x80x9cendxe2x80x9d of the flexible drive member. Therefore, significant amounts of labor are required to perform maintenance on the tensioning device and drive system.
In accordance with the present invention, a tensioning device for a drive system having a flexible drive element, such as a belt or chain, mounted on at least one driven member is provided. The tensioning device includes a first tensioning member, a second tensioning member, and a connecting member. The tensioning members each have a first side, a second side, and a contact surface for contacting the drive element. The connecting member has a length, a first end and a second end, whereby the first sides of the tensioning members are secured to the respective ends of the connecting member in a spaced relationship to one another. The second sides of the tensioning members remain unconnected to the connecting member to allow for free access to the drive element. The connecting member has at least one longitudinal contour along the length of the connecting member that reinforces the stiffness of the member. The first and second contact surfaces of the tensioning members are facing one another and are spaced apart by a distance sufficient to permit first and second runs of the drive element to pass between the tensioning members while in contact with the first and second contact surfaces, respectively. The connecting member holds the tensioning members a fixed distance from one another during operation of the drive system, such that when the tensioning device is in contact only with the drive element, the tensioning device can respond to fluctuations in load on the drive element by moving in a direction parallel to the drive element at the points of contact between the drive element and the tensioning members.
In accordance with other aspects of this invention, the longitudinal contour is formed by having at least one edge formed along the length of the connecting member, angled relative to the first side. In accordance with one aspect of the present invention, the longitudinal contour comprises a rib formed along the length of the connecting member. In accordance with still yet other aspects of the present invention, the first tensioning member is mounted on the connecting member so that it can be selectively positioned at a selected distance from the second tensioning member. This selective adjustability is provided in a preferred embodiment by a connecting member with a plurality of apertures for selectively mounting the tensioning member at a selected distance from the second tensioning member.
In accordance with additional aspects of the present invention, the connecting member is connected to the first and second sides of at least one of the tensioning members wherein the side of the tensioning device containing the said second sides of the tensioning members remains unobstructed for free access to the drive element. In accordance with further additional aspects of the present invention, the tensioning members are formed as rollers or sprockets.
A tensioning device formed in accordance with the present invention has several advantages over currently available tensioning devices. The orientation of the connecting member on only one side of the tensioning members allows the user to access the flexible drive element without disassembling the device, such as by removing a strap from one side of the tensioning device, or by removing the flexible drive element from at least one of the drive or driven members and sliding the tensioning device off that xe2x80x9cendxe2x80x9d of the flexible drive element. Therefore, significant amounts of labor are saved during the performance of maintenance on the tensioning device and drive system. In addition to being easier to maintain, the device is simpler and less costly to manufacturer. Inasmuch as a tensioning device formed in accordance with the present invention includes a single connecting member, raw material, manufacture, and assembly labor costs are all reduced compared to currently available tensioning devices utilizing two or more connecting members.
Further, the invention is advantageous since the tensioning device is able to operate with a single connecting member without having the flexible drive element disengage from the tensioning device. This is accomplished by having a longitudinal contour along the length of the connecting member that reinforces the stiffness of the member. A stiff connecting member resists any forces that may subvert the parallel alignment of the tensioning member contact surfaces, greatly enhancing the ability of the flexible member to remain engaged with the tensioning device. Thus a tensioning device formed in accordance with the present invention is economical to produce, easier to maintain, and effective.